1. Field of the Invention
The present invention relates to a code division multiplex signal transmitter and a code division multiplexing method for use in a transmission side of code division multiplex communication.
2. Description of the Background Art
Code division multiplexing (CDM) technology is used for a telecommunications network system, which can multiplex a plurality of data to be transmitted in a time slot. Since the CDM technology can be used to transmit a large amount of data while saving a communications resource such as time slots, it has mainly been put to practical use for mobile communications.
With reference to FIG. 12, an exemplified conventional CDM signal transmitter for use in CDM communication will be described. FIG. 12 is a schematic block diagram showing the exemplified conventional CDM signal transmitter disclosed in U.S. patent application publication No. US 2004/0047330 A1 to Matsuno et al., for example.
The CDM signal transmitter 12 receives a plurality (N) of channels of data S101-1, S101-2, S101-3, . . . , S101-(N−1) and S101-N to be transmitted, where N is a natural number. The data to be transmitted S101-1 to S101-N are respectively encoded to data S103-1 to S103-N by encoding circuits (EN CKT) 22 included in an encoder 20 with codes of their corresponding channels. Each encoded data S103-1, S103-2, S103-3, . . . , S103-(N−1) or S103-N is a binary signal taking its value equal to binary “0” or “1”, and is sent to an amplifier 44.
The amplifier 44 includes amplifying circuits 46, the number of which is equal to the number N of the channels. The amplifying circuits 46 amplify the amplitude of the encoded data S103-1 to S103-N to develop amplified signals S110-1, S110-2, S110-3, . . . , S110-(N−1) and S110-N, respectively. In this exemplified conventional CDM signal transmitter 12, all the amplifying circuits 46 amplify the encoded data with a common ratio so that the amplified signals S110-1 to S110-N have the amplitude levels equal to each other. The amplified signals S110-1 to S110-N developed by the amplifier 44 are sent to a multiplexer 50.
The multiplexer 50 multiplexes the amplified signals S110-1 to S110-N to produce a code division multiplex signal S111. The code division multiplex signal S111 obtained from the N channels of data to be transmitted S101-1 to S101-N will be an (N+1)-valued signal taking any one of the values 0, 1, 2, . . . , N.
The exemplified conventional CDM signal transmitter described above thus requires amplifying circuits, the number of which is equal to the number N of the channels of data to be transmitted. Therefore, an increase in the number N of the channels leads to an increase in number of amplifying circuits, thus increasing the cost for the components. In addition, it increases the size of circuitry in the multiplexer so that it is difficult to manufacture it.